This invention relates in general to a freeze drying apparatus and, more particularly, to a safety flask particularly adapted for use in freeze drying and similar laboratory procedures.
Freeze drying has been found useful in many fields, such as food technology, analysis of organic materials, and other uses. It is ordinarily used where the need exists to remove water or other vaporizable liquids from a substance without destroying its cellular structure. Freeze drying has the unique capability of allowing a controlled rate of evaporation of the vaporizable liquid from the material so that, in escaping, the velocity of the vapor particles is not so great that it will damage the residual material. Specimens or materials are usually freeze dried in either a chamber-type freeze dryer or a nipple-type freeze dryer, using discrete containers.
There are a number of prerequisites, however, that any vessel or specimen container must have before it may be used in freeze drying, in order to overcome the various problems encountered in this operation. One problem includes the stress created due to the sudden subjection of the container to the sub-zero temperatures necessary for quick freezing, which could result in the tendency to crack and/or shatter many materials.
Another problem involves the procedure employed for the application and release of the vacuum. Various types of specimens require the application of extreme care to avoid damage when the vacuum is applied or released. Should the vacuum be applied too suddenly, varying amounts of the samples may be drawn into the vacuum source. Likewise, extreme care must be taken to release the vacuum gently, or a loss of sample may result through excessive agitation by the inrushing air. In addition, the sample container must be fluid-tight in order to be satisfactory for freeze drying procedures. For the purposes of this invention, the word "fluid " will encompass both the properties of a liquid and that of a gas or vapor.
An example of a free drying apparatus which is not sufficiently protected against vacuum leakage is U.S. Pat. No. 3,293,722 (D.S. Frazer et al.) which provides only one sealing means on its connector tube and, further, depends on a threaded cap to secure such a seal. This arrangement, if properly sealed every time, would lead to a shortened life expectancy of the sealing means involved and the possibility of vacuum leakage, with the adverse consequences.
Other problems presented in freeze drying are that the solvents evaporated from the sample may be corrosive or otherwise damaging to the specimen container. Thus, while the container is generally a delicate piece of apparatus and must be handled and supported with a great degree of care to negate the danger of implosion or breakage, it is desirable that it be easy to clean after each use.